// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tty

import (
	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
	"gvisor.googlesource.com/gvisor/pkg/sentry/unimpl"
	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
	"gvisor.googlesource.com/gvisor/pkg/syserror"
	"gvisor.googlesource.com/gvisor/pkg/waiter"
)

// masterInodeOperations are the fs.InodeOperations for the master end of the
// Terminal (ptmx file).
//
// +stateify savable
type masterInodeOperations struct {
	inodeOperations

	// d is the containing dir.
	d *dirInodeOperations
}

var _ fs.InodeOperations = (*masterInodeOperations)(nil)

// newMasterInode creates an Inode for the master end of a terminal.
func newMasterInode(ctx context.Context, d *dirInodeOperations, owner fs.FileOwner, p fs.FilePermissions) *fs.Inode {
	iops := &masterInodeOperations{
		inodeOperations: inodeOperations{
			uattr: fs.WithCurrentTime(ctx, fs.UnstableAttr{
				Owner: owner,
				Perms: p,
				Links: 1,
				// Size and Blocks are always 0.
			}),
		},
		d: d,
	}

	return fs.NewInode(iops, d.msrc, fs.StableAttr{
		DeviceID: ptsDevice.DeviceID(),
		// N.B. Linux always uses inode id 2 for ptmx. See
		// fs/devpts/inode.c:mknod_ptmx.
		//
		// TODO: Since ptsDevice must be shared between
		// different mounts, we must not assign fixed numbers.
		InodeID: ptsDevice.NextIno(),
		Type:    fs.CharacterDevice,
		// See fs/devpts/inode.c:devpts_fill_super.
		BlockSize: 1024,
		// The PTY master effectively has two different major/minor
		// device numbers.
		//
		// This one is returned by stat for both opened and unopened
		// instances of this inode.
		//
		// When the inode is opened (GetFile), a new device number is
		// allocated based on major UNIX98_PTY_MASTER_MAJOR and the tty
		// index as minor number. However, this device number is only
		// accessible via ioctl(TIOCGDEV) and /proc/TID/stat.
		DeviceFileMajor: linux.TTYAUX_MAJOR,
		DeviceFileMinor: linux.PTMX_MINOR,
	})
}

// Release implements fs.InodeOperations.Release.
func (mi *masterInodeOperations) Release(ctx context.Context) {
}

// GetFile implements fs.InodeOperations.GetFile.
//
// It allocates a new terminal.
func (mi *masterInodeOperations) GetFile(ctx context.Context, d *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
	t, err := mi.d.allocateTerminal(ctx)
	if err != nil {
		return nil, err
	}

	return fs.NewFile(ctx, d, flags, &masterFileOperations{
		d: mi.d,
		t: t,
	}), nil
}

// masterFileOperations are the fs.FileOperations for the master end of a terminal.
//
// +stateify savable
type masterFileOperations struct {
	fsutil.PipeSeek      `state:"nosave"`
	fsutil.NotDirReaddir `state:"nosave"`
	fsutil.NoFsync       `state:"nosave"`
	fsutil.NoopFlush     `state:"nosave"`
	fsutil.NoMMap        `state:"nosave"`

	// d is the containing dir.
	d *dirInodeOperations

	// t is the connected Terminal.
	t *Terminal
}

var _ fs.FileOperations = (*masterFileOperations)(nil)

// Release implements fs.FileOperations.Release.
func (mf *masterFileOperations) Release() {
	mf.d.masterClose(mf.t)
	mf.t.DecRef()
}

// EventRegister implements waiter.Waitable.EventRegister.
func (mf *masterFileOperations) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
	mf.t.ld.masterWaiter.EventRegister(e, mask)
}

// EventUnregister implements waiter.Waitable.EventUnregister.
func (mf *masterFileOperations) EventUnregister(e *waiter.Entry) {
	mf.t.ld.masterWaiter.EventUnregister(e)
}

// Readiness implements waiter.Waitable.Readiness.
func (mf *masterFileOperations) Readiness(mask waiter.EventMask) waiter.EventMask {
	return mf.t.ld.masterReadiness()
}

// Read implements fs.FileOperations.Read.
func (mf *masterFileOperations) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, _ int64) (int64, error) {
	return mf.t.ld.outputQueueRead(ctx, dst)
}

// Write implements fs.FileOperations.Write.
func (mf *masterFileOperations) Write(ctx context.Context, _ *fs.File, src usermem.IOSequence, _ int64) (int64, error) {
	return mf.t.ld.inputQueueWrite(ctx, src)
}

// Ioctl implements fs.FileOperations.Ioctl.
func (mf *masterFileOperations) Ioctl(ctx context.Context, io usermem.IO, args arch.SyscallArguments) (uintptr, error) {
	switch cmd := args[1].Uint(); cmd {
	case linux.FIONREAD: // linux.FIONREAD == linux.TIOCINQ
		// Get the number of bytes in the output queue read buffer.
		return 0, mf.t.ld.outputQueueReadSize(ctx, io, args)
	case linux.TCGETS:
		// N.B. TCGETS on the master actually returns the configuration
		// of the slave end.
		return mf.t.ld.getTermios(ctx, io, args)
	case linux.TCSETS:
		// N.B. TCSETS on the master actually affects the configuration
		// of the slave end.
		return mf.t.ld.setTermios(ctx, io, args)
	case linux.TCSETSW:
		// TODO: This should drain the output queue first.
		return mf.t.ld.setTermios(ctx, io, args)
	case linux.TIOCGPTN:
		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), uint32(mf.t.n), usermem.IOOpts{
			AddressSpaceActive: true,
		})
		return 0, err
	case linux.TIOCSPTLCK:
		// TODO: Implement pty locking. For now just pretend we do.
		return 0, nil
	case linux.TIOCGWINSZ:
		return 0, mf.t.ld.windowSize(ctx, io, args)
	case linux.TIOCSWINSZ:
		return 0, mf.t.ld.setWindowSize(ctx, io, args)
	default:
		maybeEmitUnimplementedEvent(ctx, cmd)
		return 0, syserror.ENOTTY
	}
}

// maybeEmitUnimplementedEvent emits unimplemented event if cmd is valid.
func maybeEmitUnimplementedEvent(ctx context.Context, cmd uint32) {
	switch cmd {
	case linux.TCGETS,
		linux.TCSETS,
		linux.TCSETSW,
		linux.TCSETSF,
		linux.TIOCGPGRP,
		linux.TIOCSPGRP,
		linux.TIOCGWINSZ,
		linux.TIOCSWINSZ,
		linux.TIOCSETD,
		linux.TIOCSBRK,
		linux.TIOCCBRK,
		linux.TCSBRK,
		linux.TCSBRKP,
		linux.TIOCSTI,
		linux.TIOCCONS,
		linux.FIONBIO,
		linux.TIOCEXCL,
		linux.TIOCNXCL,
		linux.TIOCGEXCL,
		linux.TIOCNOTTY,
		linux.TIOCSCTTY,
		linux.TIOCGSID,
		linux.TIOCGETD,
		linux.TIOCVHANGUP,
		linux.TIOCGDEV,
		linux.TIOCMGET,
		linux.TIOCMSET,
		linux.TIOCMBIC,
		linux.TIOCMBIS,
		linux.TIOCGICOUNT,
		linux.TCFLSH,
		linux.TIOCSSERIAL,
		linux.TIOCGPTPEER:

		unimpl.EmitUnimplementedEvent(ctx)
	}
}
